In installations of this kind, it is necessary to provide at least one flow control device for controlling a stream of air through an air passage aperture. This stream of air may be fresh air, heated air, or conditioned air. The air passage aperture may be an inlet or outlet opening defined by, for example, a duct, a distribution port, or other part of the heating or air conditioning installation.
Conventional flow control devices used in these situations generally consist of pivoting flap valves, especially of the curtain or butterfly type, which can be driven in rotation either manually or by means of a motorized actuator. These flap type flow control devices have the major disadvantage that they require a large amount of space in order to permit the valve member (i.e. the flap) to be displaced. This increases the overall size of the heating and/or air conditioning installation. In addition, they give rise to a considerable resistance to the air flow, and this in turn means that quite powerful motorized actuators must be used.
It is known in addition, in particular from French patent specification No. FR 2 580 791 A, to make use of a flow control device of the type comprising a film, in the form of a flexible blind or curtain, which is rolled on two rollers which are spaced apart from each other. The film is arranged to be disposed across the air passage aperture through which the flow of air is to be controlled. To this end, the film is formed with open regions and closed regions, so that the air flow is controlled selectively by moving the film between different positions in relation to the aperture. Thus, the film can be displaced either in one direction or in the opposite direction by winding it on to one of the rollers and unwinding it at the same time from the other roller.
Known devices of this type, also referred to as film obturators, do however have the disadvantage that they are of somewhat complex structure; and they require particular adaptation of the casing of the heating or air conditioning installation as a whole, in order that the flow control device can be fitted within this casing. As a result, the structure of the casing of the installation has to be somewhat complex. In addition, it should be noted that these film obturators of known types have to be designed specially for each design of heating or air conditioning installation. Moreover, these known types of device involve lengthy and costly fitting operations.
One problem which is encountered in flow control devices of the film obturator type is to ensure good integrity of the film in the zone normally referred to as the diffusion zone. This is the zone in which the stream of air meets the film. In this connection, the film itself is a flexible element which is formed generally of textile and plastics materials, and the holes through the film that define the above mentioned open regions may be quite large: this in turn affects the strength of the film and its stiffness, i.e. its resistance to unwanted deformation. If the film is not strong enough or rigid enough, it can tend to become creased or wavy, and this is detrimental to proper functioning of the flow control device. It can also lead to vibrations or even noise, and can sometimes also lead to the film becoming jammed. In order to overcome this disadvantage, known devices of the film obturator type include film tensioning means, such as mechanical tensioners with strings and pulleys. However, these mechanisms are complex, and involve delicate adjustment.